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31.
The atmospheres and circumstellar envelopes of AGB stars are characterized by complex physical phenomena like shock waves
caused by stellar pulsation or formation of molecules and dust which often lead to a heavy mass loss and have a strong influence
on IR properties as observed by ISO. To allow a physical interpretation of various observations we have constructed improved
dynamical model atmospheres of long-period variables. In this contribution we mainly investigate the dependence of the atmospheric
structure and its variability on stellar pulsation, molecular opacities and time-dependent dust formation. IR spectra resulting
from our models are discussed in detail by Loidl et al. (1997b) and compared to ISO-SWS spectra obtained by Hron et al. (1997).
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
32.
Gerrit de Leeuw Lucinda Spokes Tim Jickells Carsten Ambelas Skjth Ole Hertel Elisabetta Vignati Susanne Tamm Michael Schulz Lise-Lotte Srensen Britta Pedersen Laura Klein K. Heinke Schlünzen 《Continental Shelf Research》2003,23(17-19):1743
The ANICE (Atmospheric Nitrogen Inputs into the Coastal Ecosystem) project addressed the atmospheric deposition of nitrogen to the North Sea, with emphasis on coastal effects. ANICE focused on quantifying the deposition of inorganic nitrogen compounds to the North Sea and the governing processes. An overview of the results from modelling and experimental efforts is presented. They serve to identify the role of the atmosphere as a source of biologically essential chemical species to the marine biota. Data from the Weybourne Atmospheric Observatory (UK) are used to evaluate the effect of short episodes with very high atmospheric nitrogen concentrations. One such episode resulted in an average deposition of 0.8 mmol N m−2 day−1, which has the potential to promote primary productivity of 5.3 mmol C m−2 day−1. This value is compared to long-term effects determined from model results. The total calculated atmospheric deposition to the North Sea in 1999 is 948 kg N km−1, i.e. 0.19 mmol N m−2 day−1 which has the potential to promote primary productivity of 1.2 mmol C m−2 day−1. Detailed results for August 1999 show strong gradients across the North Sea due to adjacent areas where emissions of NOx and NH3 are among the highest in Europe. The average atmospheric deposition to the southern part of the North Sea in August 1999 could potentially promote primary production of 2.0 mmol C m−2 day−1, i.e. 5.5% of the total production at this time of the year in this area of the North Sea. For the entire study area the atmospheric contribution to the primary production per m2 is about two-third of this value. Most of the deposition occurs during short periods with high atmospheric concentrations. This atmospheric nitrogen is almost entirely anthropogenic in origin and thus represents a human-induced perturbation of the ecosystem. 相似文献
33.
Linking vulnerability, adaptation, and resilience science to practice: Pathways, players, and partnerships 总被引:7,自引:1,他引:7
Coleen Vogel Susanne C. Moser Roger E. Kasperson Geoffrey D. Dabelko 《Global Environmental Change》2007,17(3-4):349-364
Vulnerability, adaptation and resilience are concepts that are finding increasing currency in several fields of research as well as in various policy and practitioner communities engaged in global environmental change science, climate change, sustainability science, disaster risk-reduction and famine interventions. As scientists and practitioners increasingly work together in this arena a number of questions are emerging: What is credible, salient and legitimate knowledge, how is this knowledge generated and how is it used in decision making? Drawing on important science in this field, and including a case study from southern Africa, we suggest an alternative mode of interaction to the usual one-way interaction between science and practice often used. In this alternative approach, different experts, risk-bearers, and local communities are involved and knowledge and practice is contested, co-produced and reflected upon. Despite some successes in the use and negotiation of such knowledge for ‘real’ world issues, a number of problems persist that require further investigation including the difficulties of developing consensus on the methodologies used by a range of stakeholders usually across a wide region (as the case study of southern Africa shows, particularly in determining and identifying vulnerable groups, sectors, and systems); slow delivery of products that could enhance resilience to change that reflects not only a lack of data, and need for scientific credibility, but also the time-consuming process of coming to a negotiated understanding in science–practice interactions and, finally, the need to clarify the role of ‘external’ agencies, stakeholders, and scientists at the outset of the dialogue process and subsequent interactions. Such factors, we argue, all hinder the use of vulnerability and resilience ‘knowledge’ that is being generated and will require much more detailed investigation by both producers and users of such knowledge. 相似文献
34.
Harald Behrens Susanne Ohlhorst Michel Champenois 《Geochimica et cosmochimica acta》2004,68(22):4687-4703
The solubility of CO2 in dacitic melts equilibrated with H2O-CO2 fluids was experimentally investigated at 1250°C and 100 to 500 MPa. CO2 is dissolved in dacitic glasses as molecular CO2 and carbonate. The quantification of total CO2 in the glasses by mid-infrared (MIR) spectroscopy is difficult because the weak carbonate bands at 1430 and 1530 cm−1 can not be reliably separated from background features in the spectra. Furthermore, the ratio of CO2,mol/carbonate in the quenched glasses strongly decreases with increasing water content. Due to the difficulties in quantifying CO2 species concentrations from the MIR spectra we have measured total CO2 contents of dacitic glasses by secondary ion mass spectrometry (SIMS).At all pressures, the dependence of CO2 solubility in dacitic melts on xfluidCO2,total shows a strong positive deviation from linearity with almost constant CO2 solubility at xCO2fluid > 0.8 (maximum CO2 solubility of 795 ± 41, 1376 ± 73 and 2949 ± 166 ppm at 100, 200 and 500 MPa, respectively), indicating that dissolved water strongly enhances the solubility of CO2. A similar nonlinear variation of CO2 solubility with xCO2fluid has been observed for rhyolitic melts in which carbon dioxide is incorporated exclusively as molecular CO2 (Tamic et al., 2001). We infer that water species in the melt do not only stabilize carbonate groups as has been suggested earlier but also CO2 molecules.A thermodynamic model describing the dependence of the CO2 solubility in hydrous rhyolitic and dacitic melts on T, P, fCO2 and the mol fraction of water in the melt (xwater) has been developed. An exponential variation of the equilibrium constant K1 with xwater is proposed to account for the nonlinear dependence of xCO2,totalmelt on xCO2fluid. The model reproduces the CO2 solubility data for dacitic melts within ±14% relative and the data for rhyolitic melts within 10% relative in the pressure range 100-500 MPa (except for six outliers at low xCO2fluid). Data obtained for rhyolitic melts at 75 MPa and 850°C show a stronger deviation from the model, suggesting a change in the solubility behavior of CO2 at low pressures (a Henrian behavior of the CO2 solubility is observed at low pressure and low H2O concentrations in the melt). We recommend to use our model only in the pressure range 100-500 MPa and in the xCO2fluid range 0.1-0.95. The thermodynamic modeling indicates that the partial molar volume of total CO2 is much lower in rhyolitic melts (31.7 cm3/mol) than in dacitic melts (46.6 cm3/mol). The dissolution enthalpy for CO2 in hydrous rhyolitic melts was found to be negligible. This result suggests that temperature is of minor importance for CO2 solubility in silicic melts. 相似文献
35.
Rita Loidl Josef Hron Susanne Höfner Uffe G. ørgensen Bernhard Aringer Franz Kerschbaum 《Astrophysics and Space Science》1997,251(1-2):243-246
Exploratory synthetic spectra were computed for carbon-rich long-period variables. We used dynamic model atmospheres of Höfner &; Dorfi (1997) and calculated partial pressures, absorption- and scattering coefficients as input for the spectral synthesis code of Jørgensen et al. (1992). First ISO SWS-observations of the carbon-Mira T Dra are compared with our synthetic spectra. 相似文献
36.
A coupled model, consisting of an ocean wave model and an atmospheric general circulation model (AGCM), is integrated under permanent July conditions. The wave model is forced by the AGCM wind stress, whereas the wind waves modify the AGCM surface fluxes of momentum, sensible and latent heat. We investigate the following aspects of the coupled model: how realistic are the wave fields, how strong is the coupling, and how sensitive is the atmospheric circulation to the spatially and temporally varying wave field. The wave climatology of the coupled model compares favorably with observational data. The interaction between the two models is largest (although weak) in the storm track in the Southern Hemisphere. Young windsea, which is associated with enhanced surface fluxes is generated mostly in the equatorward frontal area of an individual cyclone. However, the enhancement of the surface fluxes is too small to significantly modify the climatological mean atmospheric circulation.This paper was presented at the Second International Conference on Modelling of Global Climate Variability, held in Hamburg 7–11 September 1992 under the auspices of the Max Planck Institute for Meteorology. Guest Editor for these papers is L. Dümenil 相似文献
37.
Topography and morphodynamics in the German Bight using SAR and optical remote sensing data 总被引:3,自引:0,他引:3
Morphological changes in coastal areas, especially in river estuaries, are of high interest in many parts of the world. Satellite
data from both optical and radar sensors can help to monitor and investigate these changes. Data from both kinds of sensors
being available for up to 30 years now, allow examinations over large timescales, while high resolution sensors developed
within the last decade allow increased accuracy. So the creation of digital elevation models (DEMs) of, for example, the wadden
sea from a series of satellite images is already possible. ENVISAT, successfully launched on March 1, 2002, continues the
line of higher resolution synthetic aperture radar (SAR) imaging sensors with its ASAR instrument and now also allows several
polarization modes for better separation of land and water areas. This article gives an overview of sensors and algorithms
for waterline determination as well as several applications. Both optical and SAR images are considered. Applications include
morphodynamic monitoring studies and DEM generation.
相似文献
Andreas NiedermeierEmail: |
38.
Urban expansion and the scarcity of water supplies in arid and semiarid regions have increased the importance of urban runoff to localized water resources. However, urban catchment responses to precipitation are poorly understood in semiarid regions where intense rainfall often results in large runoff events during the short summer monsoon season. To evaluate how urban runoff quantity and quality respond to rainfall magnitude and timing, we collected stream stage data and runoff samples throughout the 2007 and 2008 summer monsoons from four ephemeral drainages in Tucson, Arizona. Antecedent rainfall explained 20% to 30% of discharge (mm) and runoff ratio in the least impervious (22%) catchment but was not statistically related to hydrologic responses at more impervious sites. Regression models indicated that rainfall depth, imperviousness and their combined effect control discharge and runoff ratios (p < 0.01, r2 = 0.91 and 0.75, respectively). In contrast, runoff quality did not vary with imperviousness or catchment size. Rainfall depth and duration, time since antecedent rainfall and event and cumulative discharge controlled runoff hydrochemistry and resulted in five specific solute response patterns: (i) strong event and seasonal solute mobilization (solute flush), (ii) event chemostasis and strong seasonal flush, (iii) event chemostasis and weak seasonal flush, (iv) event and seasonal chemostasis and (v) late seasonal flush. Our results indicate that hydrologic responses of semiarid catchments are controlled by rainfall partitioning at the event scale, whereas wetting magnitude, frequency and timing alter solute stores readily available for transport and control temporal runoff quality. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
39.
Susanne?M.?McDowellEmail author Calvin?F.?Miller Roland?Mundil Charles?A.?Ferguson Joseph?L.?Wooden 《Contributions to Mineralogy and Petrology》2014,168(1):1031
The Silver Creek caldera (southern Black Mountains, western Arizona) is the source of the 18.8 Ma, >700 km3 Peach Spring Tuff (PST) supereruption, the largest eruption generated in the Colorado River Extensional Corridor (CREC) of the southwestern United States. Within and immediately surrounding the caldera is a sequence of volcanics and intrusions ranging in age from ~19 to 17 Ma. These units offer a record of magmatic processes prior to, during, and immediately following the PST eruption. To investigate the thermal evolution of the magmatic center that produced the PST, we applied a combination of Ti-in-zircon thermometry, zircon saturation thermometry, and high-precision U–Pb CA–TIMS zircon dating to representative pre- and post-supereruption volcanic and intrusive units from the caldera and its environs. Similar to intracaldera PST zircons, zircons from a pre-PST trachytic lava (19 Ma) and a post-PST caldera intrusion (18.8 Ma) yield exceptionally high-Ti concentrations (most >20 ppm, some up to nearly 60 ppm), corresponding to calculated temperatures that exceed 900 °C. In these units, Ti-in-zircon temperatures typically surpass zircon saturation temperatures (ZSTs), suggesting the entrainment of zircon that had grown in hotter environments within the magmatic system. Titanium concentrations in younger volcanic and intrusive units (~18.7–17.5 Ma) decline through time, corresponding to an average cooling rate of 10?3.5 °C/year. The ~200 k.y. thermal peak evident at Silver Creek caldera is spatially limited: elsewhere in the Miocene record of the northern CREC, Ti-in-zircon concentrations and ZSTs are much lower, suggesting that felsic magmas were generally substantially cooler. 相似文献
40.
Julia Scharwächter Andreas Eckart Susanne Pfalzner Jens Zuther Melanie Krips Eva Schinnerer Johannes Staguhn 《Astrophysics and Space Science》2005,295(1-2):101-106
I Zw 1 and 3C 48 are two neighboring template objects at a later stage of the hypothesized merger-driven evolutionary sequence from ultra-luminous infrared galaxies (ULIRGs) to quasi-stellar objects (QSOs). Since galaxy mergers are assumed to trigger the evolution, it is important to confirm the merger properties of transitionary objects. Using multi-wavelength observations and N-body simulations, the merger histories of I Zw 1 and 3C 48 have been investigated in two separate case studies. Here, the results from both studies are compared and their relevance for the evolutionary hypothesis is discussed.This research is partly based on observations with ISAAC at the Very Large Telescope (VLT) of the European Southern Observatory (ESO) under projects 67.B-0009 and 67.B-0019. 相似文献